Field of the Invention
Phenol is a base product of petrochemistry, of which more than 5 million metric tons are produced per year worldwide. Phenol serves as starting product for numerous intermediates and finished products. A large proportion of the phenol is further processed to form phenol-formaldehyde resins. In addition, bisphenol A (2,2'-di-(4-hydroxyphenyl)propane) is prepared from phenol and acetone to a great extent, since bisphenol A has become of increasing importance as a starting product for polycarbonates and epoxy resins.
Phenol has a melting or solidification point of 41.degree. C.; it is therefore solid at the usual ambient temperatures. However, phenol is handled in solid form only in insignificantly small amounts. Phenol is customarily transported and stored as a liquid at temperatures above its solidification point. In order to keep the phenol liquid, the piping, transhipment facilities and the storage and transport vessels are customarily insulated against heat losses. An additional heating means is generally also required. Thermally insulated, treated transport and storage systems are therefore usually used.
The vessel material used is generally steel. Phenol has a tendency to discolor owing to oxidation products of phenol. If the phenol is to remain colorless for as long as possible, transport and storage systems made of stainless steel are used.
During the storage and transport of liquid phenol, care must be taken to keep the temperature below 70.degree. C., since the lower explosive limit for phenol/air mixtures is reached at a saturation temperature of approximately 73.degree. C. At storage temperatures above the flash point, the gas space in the vessel must be rendered inert by complex measures, e.g. by introducing nitrogen gas.
Another known commercial form of phenol is a mixture of phenol with water, in which case, by addition of water, in theory, a solidification point of the phenol/water mixture can be set between 0.degree. C. and 41.degree. C. However, in practice, only the concentration range of 8 to 10% by weight of water in the mixture is employed. If more water is added to the system, it divides into a water-rich and a phenol-rich phase. The phenol/water system has a miscibility gap (cf. Ullmanns Encyklopadie der technischen Chemie Ullmanns Encylopaedia of Industrial Chemistry!, 4th edition, 1979, vol. 18, p.177) below 69.degree. C. A mixture of phenol with approximately 10% by weight of water has a solidification point of approximately 13.5.degree. C.; a mixture with 20% by weight of water has a solidification point of approximately 5.degree. C. The miscibility gap of the phenol/water system at 10.degree. C. is between phenol contents of 7% by weight and 75% by weight. However, depending on climatic conditions, temperatures of 0.degree. C. and below can also occur during transport and storage of phenol. Therefore, even the addition of water to the phenol does not avoid the need in every case for the use of treatable thermally insulated vessels. Furthermore, the water, depending on the phenol application must generally be removed from the phenol again later by complex means.
The object of the present invention is therefore to provide a method for the transport and storage of phenol in the liquid phase which does not require the use of treatable thermally insulated systems under conventional transport and storage conditions.